Amoeba farms bacteria for food and weapons

There are new details about how the world’s smallest farmer picks up edible bacteria and then harvests them like crops.

The organism, a social amoeba called Dictyostelium discoideum, carries not one but two strains of bacteria. One strain is the “seed corn” for a crop of edible bacteria, and the other strain is a weapon that produces defensive chemicals.

The edible bacteria, the scientists found, evolved from the toxic one. The two strains differ by many mutations but a single key mutation, which hit an important controller in the genome of the nonfood strain, alters expression of 10 percent of its genome. This alteration increases the expression of some genes and decreases the expression of others.